1. Field of the Invention
The present invention generally relates to a method for forming a capacitor of a semiconductor device, and more specifically, to a method for forming a capacitor which prevents CMP by-products from flowing the inside of the capacitor during a CMP process for separating a storage electrode when the capacitor is formed.
2. Description of the Prior Art
FIGS. 1a to 1h are cross-sectional diagrams illustrating a conventional method for forming a capacitor of a semiconductor device.
Referring to FIG. 1a, a stacked pattern of a bitline 12 and a hard mask film 14 is formed on a semiconductor substrate 10.
Thereafter, a nitride film or an oxide film (not shown) is formed on the entire surface of the resulting structure, and spacers 16 are formed on sidewalls of the stacked pattern of the bitline 12 and the hard mask film 14 by blanket-etching the nitride film or the oxide film.
Next, a plug material is deposited on the entire surface of the resulting structure, and a storage electrode contact plug 18 is formed by planarizing the plug material. Then, a Si3N4 film or a SiON film is deposited on the entire surface of the resulting structure to form a nitride film for storage electrode 20.
Referring to FIG. 1b, an oxide film for storage electrode 22 is formed on the nitride film for storage electrode 20.
Referring to FIG. 1c, a storage electrode hard mask film 24 is formed on the oxide film for storage electrode 22.
After a photoresist film (not shown) is deposited on the storage electrode hard mask film 24, the photoresist film is selectively exposed and developed to form a photoresist film pattern 26.
Next, a pattern of the storage electrode hard mask film 24 is formed by selectively etching the lower storage electrode hard mask film 24 using the photoresist film pattern 26 as an etching mask. Then, a pattern of the oxide film for storage electrode 22 is formed by selectively etching the lower oxide film for storage electrode 22 using the pattern of the storage electrode hard mask film 24 as an etching mask.
Referring to FIG. 1d, a pattern of the nitride film for storage electrode 20 is formed by selectively etching the lower nitride film for storage electrode 20 using the pattern of the oxide film for storage electrode as an etching mask, thereby defining a storage electrode region.
The initial thickness of the oxide film for storage electrode 22 is t1 as shown in FIG. 1c. However, the thickness of the oxide film for storage electrode 22 (t2) after the etching process becomes shorter ranging from 100 to 800 Å than the thickness t1 since it is used as the etching mask during the etching process of the nitride film for storage electrode 20.
Referring to FIG. 1e, a polysilicon film is deposited on the entire surface of the resulting structure to form a conductive layer for storage electrode 28.
Referring to FIG. 1f, a gap-filling photoresist film 30 is formed on the entire surface of the resulting structure.
Referring to FIG. 1g, a CMP process is performed on the conductive layer for storage electrode 28 and the gap-filling photoresist film 30 using the oxide film for storage electrode 22 as a polishing stop layer, thereby forming a storage electrode 32.
As a result, photoresist materials for forming the photoresist film 30, CMP slurry residuals and foreign substances (represented by “D”) which are reactants of polysilicon for forming the storage electrode 32 are deposited on the gap-filling photoresist film 30 or the storage electrode 32 in the capacitor by the CMP process.
The photoresist materials which are removed by the CMP process contaminate CMP equipment, and the CMP process performed by the contaminated CMP equipment reduces yield of devices and degrades efficiency of the equipment.
FIG. 2 is a CD SEM plane photograph illustrating the result of FIG. 1g. FIG. 2 shows that the foreign substances D which are generated after the CMP process exist on the gap-filling photoresist film 30 in the capacitor or on the boundary surface of the photoresist film 30 and the storage electrode 32.
Referring to FIG. 1h, the gap-filling photoresist film 30 which remain on the resulting surface is removed by using mixture solution of H2SO4 and H2O2. Here, the foreign substance D which remain on the gap-filling photoresist film 30 in the capacitor is easily removed, but the foreign substance D deposited on the storage electrode 32 is not easily removed by a cleaning process, which causes fail of devices and degrades yield.